Evaluation of Nycodenz and Percoll density gradients for the selection of motile human spermatozoa

Two high-density media, Percoll (Pharmacia, Uppsala, Sweden) and Nycodenz (Nyegaard & Co., Oslo, Norway), were assessed for efficacy of selection of motile spermatozoa from oligozoospermic and asthenozoospermic semen samples. The results indicated initially that the media were equivalent for motile sperm selection. However, only the spermatozoa selected from discontinuous Nycodenz gradients retained their motility for at least 21 hours (60% motility compared with 5% motility). A significantly higher number of motile spermatozoa were harvested from discontinuous Nycodenz gradients than from matched control samples using the swim-up procedure (12.0 +/- 3.0 standard error of the mean [SEM] X 10(6)/ml versus 1.9 +/- 0.7 SEM X 10(6)/ml; 27 experiments, P less than 0.001). Discontinuous Nycodenz gradients may be useful for selection of motile spermatozoa from poor-quality semen for in vitro fertilization.